This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
At least some known gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air which is mixed with fuel and channeled to the combustor. The mixture is then ignited for generating hot combustion gases, and the combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
During engine operation, foreign objects may be unavoidably ingested into the engine. More specifically, various types of foreign objects, such as birds, hailstones, sand and/or rain may become entrained in the inlet of a gas turbine engine. As the foreign objects are forced through the engine, the objects may impact a blade resulting in a portion of the impacted blade being torn loose from a rotor. Such a condition, known as foreign object damage (FOD), may cause the rotor blade to contact and/or pierce an engine casing resulting in cracks along an exterior surface of the engine casing, causing possible injury to nearby personnel, and/or damage to adjacent equipment. Over time, the foreign object damage may cause a portion of the engine to bulge or deflect causing additional stresses to be induced along the entire engine casing.
To facilitate preventing such casing stresses, and to minimize the risks of injuries to personnel, at least some known engines include a metallic casing shell that facilitates increasing a radial and an axial stiffness of the engine, and to facilitate reducing stresses near any engine casing penetration. However, because such casing shells increase the overall weight of the engine, such shells may also adversely impact the engine performance.